Adaptability, competitiveness and economic thresholds of Cyperus esculentus L. in irrigated rice

As plantas daninhas s??o respons??veis por grande parte da redu????o de produtividade das lavouras de arroz irrigado. A esp??cie Cyperus esculentus, pertencente ?? fam??lia Cyperaceae, destaca-se pela adapta????o ao ambiente irrigado. Pouco se conhece sobre a habilidade competitiva da esp??cie com a cultura do arroz e qual ?? a dimens??o do preju??zo econ??mico causado. O n??vel de dano econ??mico (NDE) tem sido importante ferramenta na quantifica????o de preju??zos ??s culturas, al??m de subsidiar a tomada de decis??o de quando ?? compensat??ria a ado????o de medida de controle. As vantagens mais evidentes do uso de NDE na tomada de decis??o s??o diminui????o dos custos de produ????o, menor uso de herbicidas e, com isso, menor contamina????o do ambiente e do homem e minimiza????o do processo de sele????o que torna as plantas daninhas resistentes. Os objetivos dessa pesquisa foram o estudo do valor adaptativo, da habilidade competitiva e a determina????o do NDE de C. esculentus na cultura do arroz irrigado, pelo uso do modelo matem??tico de regress??o n??o linear derivado da hip??rbole retangular, em fun????o do ciclo das cultivares de arroz irrigado, ??poca de irriga????o e popula????o da planta daninha. Para tal, foram conduzidos estudos de adapta????o e competi????o a campo e em casa de vegeta????o no ano agr??cola 2010/11. Em geral, as cultivares de arroz estudadas possuem valor adaptativo superior a C. esculentus. Para a cultura do arroz, a competi????o intraespec??fica ?? mais importante, enquanto que para a planta daninha a competi????o interespec??fica ?? a mais pronunciada. O modelo hiperb??lico estima satisfatoriamente as perdas de produtividade que C. esculentus causa ?? cultura do arroz. A vari??vel explicativa popula????o de Cyperus esculentus ?? a que mais se ajustou ao modelo. A redu????o no ciclo de desenvolvimento da cultivar de arroz e a antecipa????o da irriga????o incrementam o potencial competitivo da cultura e, consequentemente, aumentam os NDE de C. esculentus.Weeds are responsible for most part of the reduction in rice yield. The species Cyperus esculentus, a Cyperaceae plant, stands out by adaptation to the flooded environment. Little is known about the competitive ability of the specie rice and what is the extent of the economic loss caused. The economic thresholds (ET) has been an important tool to quantify weed damage to crops, in addition to supporting decision making of when the adoption of compensatory measure of control. The most obvious consequences of the use of ET in decision making are reduction of production costs, less use of herbicides and thereby benefitting the environment and man, and minimization of the selection pressure that select weeds resistant. The objectives of this research were to study the adaptive value, the competitive ability and the determination of ET for C. esculentus on flooded rice, using mathematical model for nonlinear regression derived from the rectangular hyperbolic, depending on the cycle of rice cultivars, irrigation timing and population of the weed. Studies were conducted for adaptation and competition in the field and greenhouse in the 2010/11 growing season. In general, the rice cultivars studied have superior adaptive value than C. esculentus. For rice, the intraspecific competition is more important, while for the weed interspecific competition is more pronounced. The hyperbolic model satisfactorily estimates the yield losses that C. esculentus causes in rice. The explanatory variable is the population of Cyperus esculentus that best fit the model. The reduction in the development cycle of rice cultivar and the anticipation of irrigation, increase the competitive potential of the culture and consequently increase the C. esculentus ET